Hi Deepak,
When you execute request download in R3AR4 in CRM, it will first send the request from CRM to ERP, so a queue with queue name R3AR* will be created to trigger the request dowload. Therefore you will see an outbound queue in CRM side.
This CRM outbound queue will trigger the FM CRS_FIRST_DOWNLOAD_TRIGGER in ERP system during RFC call.
Regards,
Ellen